Republican candidates stepped up attacks against President Obama and each other in the last full day of campaigning in Iowa, where the nation's first Republican voters will decide who they want to see represent their party in November.

From churches to vineyards, candidates shook residents' hands, kissed babies and charmed voters ahead of the country's first casting call for the Republican presidential nomination.

Despite reservations about his candidacy, especially among Iowa's evangelical groups, former Massachusetts Gov. Mitt Romney tops the polls in the Hawkeye State. The latest Des Moines Register poll, released Saturday, shows Romney garnering 24 percent of support, followed closely by Rep. Ron Paul of Texas at 22 percent and former Sen. Rick Santorum of Pennsylvania at 15 percent.

Romney has regained his No. 1 status for the first time since June, after losing the spot to Texas Gov. Rick Perry, Herman Cain and Gingrich.

The biggest surprise in Iowa, however, has been Santorum, who has surprisingly surged in polls, buoyed in part by support of evangelical groups. Today, the patriarch of reality TV show "19 Kids and Counting," Jim Bob Duggar campaigned for Santorum with 12 of his 19 children.

At an event in Polk City, Duggar, a former state representative in Arkansas, told attendees that they are "not going to find a perfect candidate, unless it's Jesus Christ."

He took a shot at Mitt Romney for his Massachusetts health care plan, while Michelle Duggar recorded robocalls for Santorum, who himself has seven children.

The event went over capacity as crowds stormed in to watch Santorum give his pitch with four of his children. The former senator railed against his critics and defended his recorded but he did stumble when questioned why he endorsed Romney, how his rival, in 2008.

Santorum muddled around a bit, ultimately admitting that he "settled. But I settled for the best option, not the worst option." He added that "the issue of health care wasn't a big deal in 2008."

As candidates made their final push, Santorum became the latest target of attacks in a sign that he's gaining momentum in the Hawkeye State.

Perry, who, along with his supporters, has spent more money in Iowa on TV ads then all the other candidates combined, dubbed Santorum as "part of the problem." Referring to Santorum's vote as senator to raise the debt ceiling, Perry suggested that when it comes to the rising national debt, he is worse than President Obama.

"He's a serial 'earmarker' and matter of face, stood up as late as yesterday and said he was proud of all of the earmarks," Perry said this morning on "The Today Show." This afternoon, Perry's campaign released a web video calling Santorum "unelectable." The ad features a 2009 clip in which Santorum is seen defending earmarks.

"That's the problem in Washington, D.C. While they're scratching each others' backs on the earmarks, they're fleecing the Americans and people are tired of that."

Perry also played the electability card, citing Santorum's 2006 Senate loss in Pennsylvania as evidence that he will not be able beat Obama. Santorum, who served two terms as a House representative and two terms as a senator, lost his congressional seat to Bob Casey, son of the former Pennsylvania governor in a "wave" election in which Democrats gained six Senate seats.

"His other argument is, 'I'm the guy that can win,' and he got beat by 18 points in his last race," Perry said in an interview today with Chuck Todd on MSNBC. "I mean this guy has proven that he can't win races when it matters against a liberal Democrat."

He also pointed to Santorum's support of Democrat Arlen Specter in 2004 as a trouble spot for conservatives. Late in the day, the Perry camp circulated a Politico story that looks at Santorum's work as a consultant for a lobbying firm that represents the Human Rights Campaign and Reform Immigration for America.

Another episode in Santorum's congressional career that could hurt the GOP candidate now: an ad he made in 2006 touting his bipartisan work with liberal Democrats such as Sens. Barbara Boxer of California and Hillary Clinton of New York.

Conservatives also worry that Santorum lacks the resources to fight a drawn-out battle in late-voting states. Although he has one of the best organized networks in Iowa, he lacks that same network in New Hampshire and South Carolina, the next voting states.

Perry highlighted that concern today, saying that neither Santorum nor Rep. Michele Bachmann of Minnesota has the "national organization in place nor the fundraising ability to go forward out of Iowa."

Still, the attacks haven't deterred Santorum. The former senator cited his rise in the Iowa polls as a sign that his campaign is well positioned.

"We're in a position to do really well here. Message matters," Santorum said today, adding that money is not as important as leadership."You can't buy Iowa. You can't buy New Hampshire."

While GOP candidates went at each other, Romney shifted his focus from attacking his GOP rivals to Obama, in a clear sign that the candidate is sensing victory.

Romney today won the endorsement of 15 state representatives in New Hampshire, home of the nation's first primary. Romney's surrogates, state Republican heavyweights John Sununu and Manchester Mayor Ted Gatsas, rallied on behalf of the former Massachusetts governor as he made the rounds in Iowa.

"I don't think it's moral to pass on our obligations to the next generation. I think it's wrong and we've got to balance our budget," Romney said at a rally in Davenport, Iowa, today, attacking Obama's fiscal record.

Santorum's rise comes at the expense of Gingrich, who continued to campaign aggressively in Iowa but appeared to have resigned himself to his new, fourth-place position and admitted that Romney's negative campaign diluted his chances.

Gingrich, meanwhile, who held on to his front-runner status in Iowa and nationally for much longer than many anticipated, admitted that Romney's attack campaign chipped away at his popularity.

He told ABC News today he will "draw a very clear contrast" with Romney "every day" immediately after the Iowa caucuses.

"Everything we say will have Romney's quote, Romney's videotape, Romney's record; it'll all be based explicitly on Romney," Gingrich said in an interview in Independence, Iowa.

Romney's super PAC, Restore Our Future, has spent close to $3 million labeling the former House speaker as a Washington insider loaded down with political baggage.